Newt Gingrich's Ex-Wife Claims He Requested Open Marriage (Video)

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Things just got messier for Newt Gingrich in his bid to win the Republican presidential nomination.

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The politician's ex-wife, Marianne, has given an interview to Nightline, airing Thursday, and in an ABC News video preview, she attacks his personal code of ethics and claims he asked for an open marriage (which would allow him to be with his mistress, Callista Bisek, who's now his third wife.)

"And I just stared at him and he said, 'Callista doesn't care what I do,'" said Marianne Gingrich, in her first TV sitdown since divorcing the former House speaker in 1999.

"He wanted an open marriage and I refused."

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The couple's 18-year marriage unraveled after Gingrich was revealed to be having an affair with Bisek, a congressional aide 23 years his junior. According to his jilted former wife, his extramarital dalliances happened "in my bedroom in our apartment in Washington. ...  He always called me at night, and always ended with 'I love you.' Well, she was listening."

To pour salt on the wound, she says, he wanted a divorce three months following her diagnosis of Multiple sclerosis. (Gingrich split from his first wife, Jackie, while she was undergoing cancer treatment.)

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Gingrich's daughters from his first marriage, Kathy Lubbers and Jackie Cushman, defended their father in a letter to ABC News Wednesday, writing: "The failure of a marriage is a terrible and emotional experience for everyone involved. Anyone who has had that experience understands it is a personal tragedy filled with regrets, and sometimes differing memories of events."

"We will not say anything negative about our father’s ex-wife. He has said before, privately and publicly, that he regrets any pain he may have caused in the past to people he loves," they wrote.

Watch the Nightline preview below.